Can you hear me now?

Close up of a Great Gray OwlSomehow I’ve managed to make a good part of my living for the last decade standing around in the dark. Owls have been a source of fascination and a subject of study for me for quite a while now.  I’m not alone in that fascination. Many people are drawn to their seemingly all-knowing eyes and wise faces.

I hate to destroy any long-held beliefs, but owls aren’t really all that wise. There are many bird species (the crow family, for example) that have much greater levels of intellect.

That doesn’t mean owls are any less remarkable. This group of birds has evolved some amazing adaptations to help them make the most of their nocturnal realm.

What I find most fascinating is their ability to hear in three-dimensions. While we can perceive depth with our eyes, they can also do it with their ears.

Owl Skull (without sclerotic ring) showing ear openings.

The secret is asymmetrical ear openings. In most animals (ourselves included), the ears tend to be at approximately the same level on either side of the head. However, in the especially nocturnal owl species or ones that predominantly use hearing to locate their prey, one ear is usually higher than the other.

As a result, sounds do not reach both ears at the same time. It’s this delay that allows the bird to figure out where the sound is coming from.  They can be quite precise, detecting differences in timing up to 30 millionths of a second. When an owl hears a sound, the medulla of the brain creates a three-dimensional mental map of where it’s located. They then hone in on that point by moving their heads until both ears are hearing the sound at the same time. When they reach that point, they are facing their prey. Adjustments can be made while in flight, moving their heads until they’re lined up to strike.

Because they are operating at such a high level of precision, it’s important to have the best hearing as possible. In many owls, like this Great Gray Owl above, most of their face is made up of a disk of feathers. This facial disk acts like a satellite dish, funneling sound to the ears. Muscles under the skin allow them to adjust the shape of the disk as needed to get the best reception. Cup your hands around your ears and you’ll get an idea of how it works.

The size of this disk of feathers is a pretty good way to quickly assess just how nocturnal an owl species is. Larger disks, relative to the overall size of the face (like in Boreal Owls or Barred Owls), means that the species tends to hunt mostly at night.

Great Grays are a bit of an exception.  They have huge facial disks, but hunt mainly at dawn and dusk. These owls, however, hunt prey that are hidden by layers of snow in the winter. Like hunting in the dark, they can use their ears to pinpoint a vole running under the snow up to 150 metres away! It gives a whole new meaning to good reception.

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